Installing and Testing Multi-Bar High Capacity Rock Tiedowns-PPT Presentation

PPT Presentation

Pdf Summary

The presentation describes the installation and testing of high-capacity, multi-bar rock tiedowns for the One Manhattan West tower, located between 31st and 33rd Streets along 9th Avenue in Manhattan. Because the building’s core was relatively narrow, tiedowns were needed to provide lateral support while optimizing the foundation’s size and layout. The highly competent Manhattan mica schist allowed relatively narrow footings.<br /><br />The installation sequence involved drilling 16-inch-diameter holes, placing bundled DCP threadbars, tremie grouting, allowing the grout to cure, and then installing, testing, and locking off the anchors. Tiedowns were typically 63 feet long, with some extending 83 feet.<br /><br />Work proceeded under tight site and schedule constraints, including drilling while rock excavation continued nearby. Limited working space affected equipment access, spoil removal, and bar installation. Unpredictable geology required several drilling approaches. When air drilling and a tri-cone bit failed to return cuttings, camera inspection identified a rock void; casing advanced with a Rotoloc under-reamer bypassed it.<br /><br />Testing the high-capacity anchors was difficult because suitable jacks were scarce and the three-bar arrangement made uniform loading challenging. Uneven loading caused bars to splay or pinch and damaged test plates. Some anchors showed excessive or inelastic movement and lost capacity; failed anchors were pulled individually to identify the problem. One anchor in a group retained elastic behavior and was accepted, while two failed anchors were replaced.<br /><br />The project demonstrated that successful tiedown installation depended on adapting drilling methods to changing ground conditions, managing demanding site logistics, and carefully addressing load distribution during testing.

Keywords

One Manhattan West

high-capacity tiedowns

multi-bar rock anchors

Manhattan mica schist

foundation support

tremie grouting

DCP threadbars

anchor testing

drilling challenges

rock voids